Transesophageal echocardiography device

ABSTRACT

In a device for transoesophagal echocardiography, an ultrasound transformer (1) is used to make a sequence of layer images for a plurality of parallel sectional planes with the aid of an ultrasonic diagnostic device (8). The layer images made during one cardiac cycle with the image repetition rate of the ultrasonic diagnostic device (8) are stored in a buffer store (34) and transferred to a main store (48) with the aid of a selection stage (49) to generate three-dimensional sets of images only when a locating device (13), and ECG device (24) and a respiration detector (54) generate release signals which are allocated to a constant spatial probe position, a constant R--R interval distance and a constant respiratory state. The content of the main store (48) is evaluated with the aid of an image processing system (56), whereby sectional images may be calculated, especially for any sectional plane, and displayed on a monitor (31).

The invention is a transesophageal echocardiography device with aflexible ultrasound probe with an attached ultrasound transducer for thegeneration of multiplanar images of a patients' heart, which isconnected to an image processing system via a control and evaluationdevice.

A transesophageal echocardiography device described in Roy W. Martin etal., An Endoscopic Micromanipulator for Multiplanar TransesophagealImaging, Ultrasound in Med. and Biol. Vol. 12, Nr. 12, pp. 965-975, 1986and produces three-dimensional reconstructions of a cardiac ultrasoundimage by recording a multitude of sectional images with the help of anultrasound transducer attached to the front of an endoscope. Thetransducer can be swung horizontally around the longitudinal axis of theendoscope producing a multitude of tomograms whose assigned sectionplanes run diagonal to each other. This affects the geometrical andoptical qualities of the image data received, resulting in inferiorquality, a small, unfavorably distributed scanning volume. Furthermore,the scans cannot be reproduced, making it impossible to achieve thethree-dimensional image quality necessary for comparative studies.

An essay by Michael Schluter et al., Transesophageal Two-DimensionalEchocardiography: Comparison of Ultrasonic and Anatomic Sections, TheAmerican Journal of Cardiology, Vol. 53, pp. 1173-1178, 1984, describesa transesophageal echocardiography device which generates horizontaltomograms. Tomographic sections through the heart are generated bymoving and turning a gastroscope within the esophagus. The necessity ofmanually moving the gastroscope--a movement which cannot bereproduced--makes it impossible to generate three-dimensional plasticimages from two-dimensional tomograms.

U.S. Pat. No. 4,327,738 describes an endoscopic process and device forultrasound-B-image scans. The ultrasound transducer is attached to therigid front part of an otherwise flexible tube. A difficult-to-reproducere-positioning is required to produce multiplanar tomograms, makingexact three-dimensional reconstructions of the scanned organsimpossible.

Starting from said technology, the invention's purpose is to create atransesophageal echocardiography device for the generation ofreproducible topographic information about the heart and its movements.

The invention solves this task with the help of the followinginnovations: an ultrasound transducer for scanning a series of parallelsection planes of the heart is attached to a sliding rail progressivelymoved axially along a straight line inside the ultrasound endoscopydevice; a temporary memory allows for the storage of at least onetomogram when scanning each section synchronous with the cardiac phases;a main memory for at least one three-dimensional image composed of aseries of parallel tomograms is used, whose data input port is connectedto the data output port of the temporary memory via one selection optionthrough which the individual tomograms associated with consecutivecardiac cycles of a series of parallel tomograms can only be transferredto the main memory if the cardiac cycles are of the same length; and anadvance signal will not move the ultrasound transducer into the nextsection until the temporary memory data are transferred to the mainmemory.

The progressive movement of the ultrasound transducer along a straightline leads to the generation of parallel section planes and equallyparallel tomograms. The ultrasound transducer is located on a slidingrail in the distal end of the ultrasound endoscopy device (an esophagusprobe) and can be moved axially. The esophagus probe is flexible tofacilitate insertion into the esophagus in the course of transesophagealechocardiography. However, the distal end is stiff, in order toprecisely orient the scanning planes. This is achieved with the help ofa multitude of guiding links, which are pulled face to face beforescanning the section planes. When stiff, these guiding links links forma straight and stable guide canal in which the sliding rail with theultrasound transducer can be moved gradually along a straight line.

A manipulation device is planned for moving the sliding rail as well asfor stiffening the distal end of the esophagus probe. This deviceincludes an intermittent motor whose forward motion is synchronized byevaluating an ECG.

The device has a memory storage buffer, which allows for the storage ofa multitude of tomograms belonging to the same section plane butdifferent intervals or phases of a cardiac cycle. When the patient has aconstant heart and respiration rate, and the location of the esophagusprobe is stable, the tomograms stored in the temporary memory aretransferred to the main memory, which combines the tomograms belongingto the same cardiac phases of consecutive cardiac cycles intothree-dimensional image data sets. This means that the main memorycontains a series of three-dimensional reconstructions of the heart ordata cubes for each increment of axial advance by the ultrasoundtransducer in the esophagus in accordance with the chronologicalresolution of a cardiac cycle or the image repetition rate of theultrasound device.

A selection option exists between intermediate and main memory to assurethat only tomograms recorded under stable conditions are combined intothree-dimensional image data sets. Only when the data contained in thememory storage buffer meet the necessary criteria for transfer into themain memory, is the sliding rail with the attached ultrasound transduceradvanced by the intermittent motor and one can head for the adjacentsection plane.

A practical model of the invention would contain a device for recordingelectrocardiograms, which would serve two purposes: it would synchronizethe advance of the motor and synchronize or trigger the images persection plane which are produced at different times during a cardiaccycle. The recorded electrocardiogram furthermore helps to determine thetime interval between the consecutive R waves of an ECG and to recordand monitor a constant heart rate, i.e. cardiac cycles of constantlength. This assures that the tomograms consecutively recorded within afixed time grid are assigned to the same phases of a cardiac cycle. Ifthe cardiac cycle were to become shorter due to the heart beatingfaster, for example, the n^(th) tomogram would no longer be assigned tothe originally assigned cardiac phase, but to a later phase, meaningthat a three-dimensional image data set would contain tomograms whichwere recorded at different cardiac phases. However, such an image dataset is unusable due to the movement of the heart.

The practical improvements and further developments of the invention arethe subject of subordinate claims.

Following is a more detailed description of the invention with the helpof a practical sample.

FIG. 1 shows a schematic representation of the invented device fortransesophageal echocardiography,

FIG. 2 shows a three-dimensional view of the esophagusscope or distalend of the endoscopic device in two different positions near the heartto be monitored,

FIG. 3 shows a schematic and graphic illustration of the invention'soperating logic and

FIG. 4 shows a schematic depiction to illustrate the generation of anarbitrary section plane through a three-dimensional image of a heart.

The transesophageal echocardiography device depicted schematically inFIG. 1 is equipped with an ultrasound head (1), for example in the formof a mechanical sector scanner or phased array, which can be guidedaxially alongside the front end of an esophagus probe (2),which--together with a heart (3)--is depicted in two different positionsin a simplified illustration in FIG. 2. The esophagus probe (2) has adistal end (4) with flexible tubing (5), which holds together amultitude of rigid guiding links (6). The distal end (4) can easily bebent due to the elasticity of the flexible tubing (5), as illustrated inFIG. 2 by the part of the esophagus probe (2) which is bent to theright.

On the inside of the guiding links (6), a guide canal was designed inwhich a sliding rail (not depicted in the illustration) with theattached ultrasound head (1) can be moved axially down the length of thecanal. To guarantee the stretching and stiffening of the distal end (4)for a precise orientation of the scanning planes of the ultrasound head(1), the guiding links have 6 holes through which a tension wire (7)extends, which can be tightened with the help of a Bowden pull wire.This helps to press the individual guiding links (6) against each otherto assure precise guidance of the sliding rail for the ultrasound head(1). When the guiding links (6) are tightened with the help of thetension wire (7), they are pressed together face-to-face as illustratedon the left side of FIG. 2, leading to a stiffening and alignment of thedistal end (4) along a straight line. After aligning the distal end (4)as illustrated on the left side of FIG. 2, a multitude of tomogramscorresponding to the section planes defined by the position of theesophagus probe (2) and ultrasound head (1) are recorded with the helpof the ultrasound head (1) and the attacked ultrasound diagnostic device(8). This is done as soon as the patient has adjusted to the insertedesophagus probe (2) and his heart and respiration rate, and the positionof the esophagus probe (2) are stable.

Since the position of the section planes through the heart (3) dependson the position of the esophagus probe (2), (which can be directlydeduced from FIG. 2), a device for the detection of the probe's positionwithin the patient's body is added to ensure that all section planes forthe tomograms to be recorded and stored are truly parallel. This isachieved with the help of a longitudinal coil (9) and a cross coil (10),attached to one of the guiding links (6) or the front end of theesophagus probe (2) and further attached to a spatial coordinatedetector (13) via two cables (11 and 12).

Both the longitudinal coil (9) and cross coil (10) are located withinthe field of two orthogonally oriented induction loops (14 and 15),which are alternately timed with the help of a pulse generator (16) inorder to produce a stable system of coordinates and which inducedifferent voltages with the help of the longitudinal coil (9) and thecross coil (10), depending on the position of the esophagus probe (2).These voltages are analyzed in the spatial coordinate detector (13).

The spatial coordinate detector (13) does not only locate the presentposition of the esophagus probe (2), but provides a continuous detectionas well as a frequency analysis in regard to the different orientationsand positions, so that a favored position or standardized direction canautomatically be determined as soon as the patient has calmed down andthe tomograms are being recorded.

At the output port of the spatial coordinate detector (13), a releasesignal is heard every time the desired most frequently used position ofthe esophagus probe (2) is achieved. At this most frequent or normallyused position of the probe, the majority of recorded tomograms isusually generated from parallel section planes. The induction loops (14and 15) are integrated into the patient's gurney, one of the inductionloops being parallel to the plane formed by the surface of the gurneyand the other one being integrated in a sidewall at a right angle tothis plane. The induction loops (14 and 15) define a fixedthree-dimensional system of coordinates, which is the point of referencefor the position of the section plane which is being scanned with thehelp of the ultrasound head (1).

Each time a section plane or section of the heart is scanned and severaltomograms have been generated for an assigned section or section planeat different phases of a cardiac cycle, the ultrasound head (1) is movedin the direction of an arrow (18) with the help of an intermittent motor(19). The intermittent motor (19) is connected to the rail carrying theultrasound head (1) by a Bowden pull wire (65); this makes it possibleto retract the ultrasound head (1) axially a distance of 0.5 mm aftereach cardiac cycle. This results in the generation of 210 section planesfor a distance of 10.5 cm. These section planes are at right angles tothe longitudinal axis of the esophagus probe (2) and go through thenearby heart (3). The forward motion of the intermittent motor (19) issynchronized with the ECG. The synchronization signals derived from thepatient's ECG are generated by a computer (20) and transmitted via asynchronizing line (21) to the intermittent motor (19) and itselectronic controls.

The patient's ECG is recorded with the help of electrodes (22, 23),which are connected to an ECG device (24). The ECG device (24) isconnected to an ECG input port (25) on the computer (20), which alsocontrols the components of the device shown in FIG. 1. The first outputport (26) of the ECG device (24) is also connected to a control inputport (27) of the ultrasound diagnostic device (8) to control thegeneration of multiplanar images by triggering the R waves in the ECG.

As soon as a trigger impulse is fed into the control input port (27),the ultrasound head (1) starts scanning the section plane assigned tothe ultrasound head according to its position and orientation and inkeeping with the image repetition rate of the ultrasound diagnosticdevice, in order to record tomograms (41) at different cardiac phaseswithin a cardiac cycle (FIG. 3). To achieve this, the ultrasound head(1) is connected to the ultrasound diagnostic device (8) via asignalling line (28). At the first image output port (29) of theultrasound diagnostic device (8), the individual tomograms (41) arefound as signals and can be transferred to the monitor (31) via a videoline (30). The monitor (31) allows for the continuous observation of thetomograms 41) which are depicted in quick succession. Depending on theindividual ultrasound diagnostic device (8), the recording of a tomogramtakes 13 msec., with the tomograms (41) shown at intervals of approx. 33msec. For a cardiac cycle of 0.8 sec, approximately two dozen tomograms(41) can thus be recorded per cardiac cycle.

The second image output port (32) of the ultrasound diagnostic device(8) is connected to the data input port of a memory storage buffer (34)via a data line (33). Using an address line (35), the computer (20)selects the memory storage buffer locations in such a way that thetomograms (41) which are generated sequentially at different timeswithin a cardiac cycle can be stored in the memory storage buffer (34)independent of the individual heart rate of the patient or his/herrespiration and the position of the probe.

FIG. 3 illustrates in exploded view the functioning of thetransesophageal electrocardiography devices shown in FIG. 1 in modularmimic display. Next to the heart (3), one can see the esophagus probe(2) and the ultrasound head (1) which can be moved in the direction ofthe arrow (18), thus allowing the scanning of sectors of the parallelsection planes (36,37). An arrow (38) marks the difference between thesection planes (36 and 37) after starting the intermittent motor (19),which is connected to the sliding rail carrying the ultrasound head (1)by a Bowden pull wire.

Using the control logic stored in the computer (20), the transesophagealechocardiography device's components depicted in FIG. 1 function asdepicted in FIG. 3.

In FIG. 3, one can see the wave pattern (39) of an ECG and especiallythe R wave (40), which occurs at the beginning of a cardiac cycle.Tomograms (41), which are assigned to the section plane (37) atdifferent intervals or cardiac phases of a cardiac cycle as illustratedin FIG. 3, are recorded every 30 or 33 msec. during a cardiac cycle withthe help of the ultrasound head (1) and ultrasound diagnostic device(8). The tomograms (41)--depicted in schematic view in FIG. 3--whosenumber varies between 1 and several dozen, are transferred to the memorystorage buffer (34) with the help of the computer's (20) control logic,with the address line (35) releasing memory areas (42) sequentiallyassigned to individual tomograms (41).

Since the tomograms (41) of a section plane, especially of section plane37, were recorded at different times or phases of a cardiac cycle, theyare distributed to data cubes (43 to 47) as illustrated in FIG. 3. Thesedata cubes are implemented by the main memory (48). FIG. 3 illustrateshow the tomograms (41), recorded at different times of a cardiac cyclebut belonging to the same section plane, are distributed to the datacubes (43 to 47) of the main memory (48) by the memory storage buffer(34). One can see that, after a complete scan of the heart volume, thedata cubes (43 to 47) contain complete, three-dimensional images whichwere generated by combining tomograms (41). During this process, eachdata cube (43 to 47) is assigned a different cardiac phase within acardiac cycle. Even though the ultrasound diagnostic device (8) does notallow for the complete scanning of the total heart (3) volume within aperiod of time neglectable compared to the heart's movement, each datacube (43 to 47) contains a three-dimensional still image of the completeheart.

In the present example, it was assumed that no changes occurred inregard to the orientation of the esophagus probe (2), the heart andrespiration rate of the patient during a number of cardiac cyclescorresponding to the number of tomograms (41) in one of the data cubes(43 to 47). Since this is impossible to achieve in practical operation,the selection option (49) depicted in FIG. 1 was added to the controllogic depicted schematically in FIG. 3.

The selection option (49) connects the output (50) of the memory storagebuffer (34) to the data input (51) of the main memory (48). If theselection option (49) is turned on, the tomograms (41) stored in thememory areas (42) are sequentially transferred to the data cubes (43 to47), depicted in schematic view. However, should there be no releasesignal at the output port (17) of the spatial coordinate detector (13),the selection option (49) is blocked with the help of the ultrasounddiagnostic device (8) and stored in the memory storage buffer (34). Thememory storage buffer 34) keeps on being overwritten with a new set oftomograms (41) until the selection option allows to switch through tothe main memory (48).

The ECG device (24) is also connected to an assigned input port of theselection option (49) by a release line (53). The release line (53) isonly active if the ECG device (24) has established that the R--Rinterval has remained constant within a tolerance of ± 5%. The ECGdevice (24) establishes automatically at which interval length thereshould be a release. This release should occur particularly if thepatient's respiration is regular and his medium heart rate is stable,approximately one minute after insertion of the esophagus probe.

A respiration detector (54), which can be connected to the ECG device(24), supervises the patient's respiration curve and generates a releasesignal for the selection option (49) using another release line (55)when the patient's respiration rate is stable.

The above observations show that the data are only transferred from thememory storage buffer (34) to the main memory (48) if the R--R interval,the patient's respiration and the position of the probe are stable.

FIG. 1 shows furthermore that the computer's (20) task is to admit theoutput signals of the detection device (13), the ECG device (24) and therespiration detector (54). The computer (20) controls the order of thefunctions of the transesophageal echocardiography device shown in FIG. 1by analyzing the different input signals.

The main memory (48) and the computer (20) are connected to a digitalimage processing system (56), as illustrated in FIG. 1. The controllines (57 and 58) connect the computer (20) to the main memory (48) andthe image processing system (56). The output of the main memory (58) isconnected to the input (59) of the image processing system.

In FIG. 4, the cardiac phase-synchronous, three-dimensional images (60to 64) stored in the main memory (48) are depicted as data cubes of amultitude of voxel. The three-dimensional images (60, 61, 62, 63 and 64)consist of isotropic cubic data sets with each image layer consisting of256×256 pixel for example. 8 bit may be used to depict the picturehalf-tone of the scanning elements or voxel.

If the three-dimensional image (60) is stored in the image processingsystem (56), the image processing system (56) allows for the drawing ofan arbitrary section plane (66) through the data set depicted as a cubein FIG. 4 and for the determination of the new sectional image (67). Theorientation of the assigned section plane (66) does not necessarilycorrespond to the relative position of either section plane 36 or 37.The section image (67) can then be transferred to the monitor (31)through an output port (68) of the image processing system (56) and bedepicted on its monitor as illustrated in FIG. 4.

We claim:
 1. An ultrasound endoscopy device for transesophagealechocardiography, comprising;an ultrasound transducer, for scanning aseries of parallel section planes of the heart with ultrasonic energy,converting ultrasound scans into electrical signals, the electricalsignals being analogs of the scanned series of parallel section planes,and transmitting the electrical signals, the ultrasound transducer beingslidably mounted upon a sliding rail situated in the interior of thedevice, such that the transducer may be linearly moved along the slidingrail of the device; ultrasound diagnostic means for receiving analogsignals of said series of parallel section planes, converting the analogsignals into signals in the form of tomograms and transmitting thesignals; and an image processing system for receiving the signals in theform of tomograms from the diagnostic means, the image processing systemcomprising,a memory storage buffer capable of storing at least one saidtomogram in synchronization with the cardiac phases when scanning eachsaid section plane; a main memory for storiong at least onethree-dimensional image composed of a series of parallel ones of saidtomograms; data selection and transmission means interconnecting a dataoutput port of said memory storage buffer to a data entry port of saidmain memory, said data selection and transmission means selectingindividual ones of said tomograms assigned to consecutive cardiac cyclesand transmitting such to said main memory only in those instances wheresaid individual tomograms correspond to cardiac cycles having the sameduration; and means for preventing the movement of the ultrasoundtransducer to the next one of said section planes until a successfultransfer of data from said memory storage buffer to said main memory. 2.The ultrasound endoscopy device of claim 1, and further including:an ECGrecording device for controlling the progressive movement of theultrasound probe along the sliding rail.
 3. The ultrasound endoscopydevice of claim 2, wherein:said ECG recording device includes a dialgauge for determining the R--R intervals of consecutive cycles as wellas the frequency distribution of the duration of the R--R intervals;said data selection and transmission means transmits an individualtomogram upon receiving a release signal from said ECG recording device;said ECG recording device sends a release signal to said data selectionand transmission means when the contents of said memory storage bufferconform to a preselected constant R--R interval.
 4. The ultrasoundendoscopy device of claim 3, wherein:said memory storage buffer has thecapacity to store a plurality of said tomograms assigned to differentcardiac phases of a cardiac cycle; and said data selection andtransmission means outputs said multiple tomograms from said memorystorage buffer in synchronization with the cardiac phases at eachsection plane positioning of the ultrasound transducer in achronological series of said three-dimensional images selected for saidmain memory, said three-dimensional images corresponding to consecutivephases of a cardiac cycle.
 5. The ultrasound endoscopy device of claim1, and further including:a spatial coordinate detector for determiningthe position of a distal end of the ultrasound endoscope, said distalend being the portion of the ultrasound endoscope in which said slidingrails are contained.
 6. The ultrasound endoscopy device of claim 5,wherein:said coordinate detector permits recording of a frequencydistribution of said positions, and said means for preventing themovement provide a release signal only in response to a preselectedconstant set position of said distal end.
 7. The ultrasound endoscopydevice of claim 5, wherein the device is carried on a gurney, and:saidspatial coordinate detector includes two coils positioned at rightangles to each other in said distal end, and two alternately alignedinduction coils, one of which is embedded in the cover of the gurney andthe other in a side wall arrayed at right angles to the surface of thegurney, the combined generated magnetic fields operating to establish afixed system of coordinates.
 8. The ultrasound endoscopy device of claim1, and further including:monitor means for monitoring the respirationpattern of the patient, being connected to said means for preventingmovement, said monitor means blocking said movement under conditionswhere said respiration pattern is unstable.
 9. The ultrasound endoscopydevice of claim 1, wherein:said main memory is controlled by a computer,said computer including display means and being adapted to display saidtomograms juxtaposed with said three dimensional images upon saiddisplay means.
 10. The ultrasound endoscopy device of claim 9,wherein:said computer includes programming means for determining anddisplaying the measurements of the heart, and, in particular, fordetermining the volumes of the different ventricles of the heart, thethickness of the cardiac wall, the mass of the cardiac muscles, changesin cardiac walls in comparative studies and movements of the cardiacwalls during a cardiac cycle.